The present invention relates to diode oscillators and in particular to planar, dielectric resonator controlled IMPATT diode oscillators.
The advantages in the use of dielectric resonators in microwave integrated circuits result from the combination of properties that they possess. They offer low-cost, high-quality resonators which are small and which approximate lumped resonant elements for use in integrated microwave circuits. They fill a gap between waveguide and stripline technologies by providing Q's and temperature stabilities approaching those of Invar (TM) cavity resonators. They offer versatility and are adaptable to various microwave structures and coupling configurations.
Using these dielectric resonators in conjunction with such active devices as bipolar transistors, FET's and Gunn diodes, planar oscillators have been developed that have high frequency stability and low noise performance.
However, to date the open literature has reported few planar, dielectric resonator controlled oscillator circuits for an IMPATT diode and these few have been successful only to a limited degree. Due to the difficulty of satisfying all of the necessary constraints in realizing a successful IMPATT diode planar oscillator circuit, existing circuits have to compromise stability, have to tolerate noise and yet are not readily reproducible.
In general, it is difficult to sustain oscillation with Si IMPATT diodes due to moding which occurs as a result of the large frequency bandwidth over which negative resistance can be obtained. The problem of moding becomes even worse when GaAs IMPATT diodes are used. Consequently, a controlled impedance seen by the active device is required over the entire negative resistance frequency range.
Applications of IMPATT diodes in planar circuits are further limited because of the extremely low magnitudes (1 to 2 ohms) of the negative resistance. Impedance transformation ratios (output/IMPATT diode) of up to 50:1 are required.
In order to retain the efficiency of the IMPATT diode it is desirable to independently control the second harmonic as well as the fundamental loading.
Finally, to realize a temperature stable planar oscillator using IMPATT diodes, or any other active devices, it is necessary to incorporate a dielectric resonator as the frequency controlling element. This has to be done while retaining control of all the other characteristics discussed above.